Three quiescent prominences were observed in the Ca ~I K-line and a fourth one also in the H-line at Oslo Solar Observatory, Harestua, and reduced by Rustad (1974) and by Engvold et al. (1980). These data are used to study the distribution of the line-of-sight velocity component, N(uo). It is pointed out that in a stationary and isotropic case, N(uo) should be a gaussian distribution. For each of the sets of measurements gaussians were therefore fitted by a least square procedure. The range in observed velocities varies considerably between the prominences. For the best observed prominence more than 70% of the kinetic energy is in the supersonic range. In the other cases none or only an insignificant part of the observations exceed the velocity of sound. Considerable deviations from gaussian distributions are apparent for the smallest velocities. This distortion shows up conspicuously in the slope of the energy spectrum, a parameter that may be used as a rough measure of spectral resolution.
If it is assumed that we have to do with MHD-turbulence as described by Kraichnan (1965), a characteristic relationship should exist between velocity and eddy size. When supersonic velocities are present, compressibility effects may severely alter this relationship. The possibility of observational confirmation is discussed.
If a turbulent velocity field is indeed present, the heat conductivity and other transport coefficients may be significantly altered as compared to the atomic values.
I. Observations and Reduction of the Material
A large quiescent prominence was observed at the eastern limb of the Sun on May 30th, 1978, in position 55 ~ N, 90 ~ E. A series of Ca II K-line spectra, with the slit placed at different positions in the prominence, was obtained by O. Andreassen at Oslo Solar Observatory, Harestua. The prominence was later visible on the disk as a large filament with pronounced arc structure. From this material Engvold et al. (1980) selected 17 spectra, taken within an interval of about one hour, and used the data to study the influence of spatial resolution on the line widths and shifts. They subtracted the scattered light from the observations and measured the line displacement at equidistant points along the slit. Measurements were carried out in 2386 points. By later averaging over 15 adjacent points, a reduced resolution-corresponding to about 15 second of arc-was simulated. This set contained 170 averaged displacements. A third set, selected from the best spectra as judged from visual appearance, consisted of 933 measured shifts. The prominence is referred to as E.W.W. in the following. Similar measurements were carried out by Rustad (1974) on spectra of three quiescent prominences that he observed at Harestua, the first one on April 29, 1971 (15 ~ N, 90~ in the K-line referred to as R1 in the following. Another series in the K-line R2, on August 11, 1972 (40 ~ S, 90 ~ E), and finally on April 5,